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9.2 Geometry Optimization Job Controls

9.2.4 Optimize Job Examples

(July 14, 2022)

Example 9.1  Optimization in Z-matrix coordinates. The input must be specified in Z-matrix format with coordinates specified. In the example below there are two coordinates representing the bond length and bond angle of a water molecule.

$molecule
   0 1
   O
   H 1 r
   H 1 r 2 ang

   r   0.95
   ang 104.5
$end

$rem
   JOBTYPE           OPT
   METHOD            HF
   BASIS             STO-3G
   GEOM_OPT_COORDS   2
$end

Example 9.2  Geometry optimization of a triflate anion that converges to an eclipsed conformation, which is a first order saddle point. This is verified via the finite difference Davidson method by setting GEOM_OPT_CHARAC to TRUE.

$molecule
   -1 1
   C  0.00000 -0.00078  0.98436
   F -1.09414 -0.63166  1.47859
   S  0.00000  0.00008 -0.94745
   O  1.25831 -0.72597 -1.28972
   O -1.25831 -0.72597 -1.28972
   O  0.00000  1.45286 -1.28958
   F  1.09414 -0.63166  1.47859
   F  0.00000  1.26313  1.47663
$end

$rem
   JOBTYPE                    opt
   METHOD                     BP86
   GEOM_OPT_DMAX              50
   BASIS                      6-311+G*
   SCF_CONVERGENCE            8
   THRESH                     14
   SYMMETRY                   FALSE
   SYM_IGNORE                 TRUE
   GEOM_OPT_TOL_DISPLACEMENT  10
   GEOM_OPT_TOL_ENERGY        10
   GEOM_OPT_TOL_GRADIENT      10
   GEOM_OPT_CHARAC            TRUE
$end

Example 9.3  TS search for alanine dipeptide rearrangement reaction beginning with a guess structure converges correctly. The resulting TS structure is verified using the finite difference Davidson method.

$molecule
   0    1
   C          3.21659       -1.41022       -0.26053
   C          2.16708       -0.35258       -0.59607
   N          1.21359       -0.16703        0.41640
   C          0.11616        0.82394        0.50964
   C         -1.19613        0.03585        0.74226
   N         -2.18193       -0.02502       -0.18081
   C         -3.43891       -0.74663        0.01614
   O          2.19596        0.25708       -1.63440
   C          0.11486        1.96253       -0.53088
   O         -1.29658       -0.59392        1.85462
   H          3.25195       -2.14283       -1.08721
   H          3.06369       -1.95423        0.67666
   H          4.20892       -0.93714       -0.22851
   H          1.24786       -0.78278        1.21013
   H          0.25990        1.31404        1.47973
   H         -2.02230        0.38818       -1.10143
   H         -3.60706       -1.48647       -0.76756
   H         -4.29549       -0.06423        0.04327
   H         -3.36801       -1.25875        0.98106
   H         -0.68664        2.66864       -0.27269
   H          0.01029        1.65112       -1.56461
   H          1.06461        2.50818       -0.45885
$end

$rem
   JOBTYPE              freq
   EXCHANGE             B3LYP
   BASIS                6-31G
   SCF_MAX_CYCLES       250
   SYMMETRY             false
   SYM_IGNORE           true
$end

@@@

$molecule
   read
$end

$rem
   JOBTYPE              ts
   SCF_GUESS            read
   GEOM_OPT_DMAX        100
   GEOM_OPT_MAX_CYCLES  1500
   EXCHANGE             B3LYP
   BASIS                6-31G
   MAX_SCF_CYCLES       250
   GEOM_OPT_HESSIAN     read
   SYMMETRY             false
   SYM_IGNORE           true
   GEOM_OPT_CHARAC      true
$end